Speed Limit Sign
MUTCD R2-1
Do not drive faster than the posted speed limit.
What it looks like
A vertical white rectangle with black legend reading SPEED LIMIT above the maximum posted number in large black figures.
When you'll see it
Posted along highways, arterials, and residential streets, especially where the legal maximum speed changes.
What to do
You must not drive faster than the number shown, and you should go slower when weather, traffic, or road conditions demand it.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.